Abstract
There are currently no techniques available to monitor the microstructural condition of power station steel components in-service (i.e. at elevated temperatures). This problem will become more acute as coal-fuelled power stations are being developed to operate at higher pressures and temperatures to provide greater efficiency; supercritical power stations could produce output efficiencies of 45 to 50 %, compared to subcritical power stations with efficiencies of 30 to 35 %. Operation at 620 deg C is now possible, with further temperature increases to 700 deg C planned by the year 2014. Supercritical power stations also emit up to 25 % less carbon dioxide into the environment (a one percent increase in efficiency gives a two percent drop in emissions such as carbon dioxide, and nitrogen and sulphur oxides). Currently the condition of power station components is monitored during shut down periods, when insulating lagging layers are removed and replicas from the component surface are made. These replicas are examined to determine the microstructural state (degree of degradation, e.g. through carbide population changes) and whether creep cavitation has initiated. Components are removed from service and replaced when end of predicted service life is reached or significant cavitation is detected. However, as the component condition can only be checked during a scheduled shut down period, sections are often replaced prematurely. If failure of a component occurs the economic impact is severe (an unplanned shutdown is estimated to cost approximately 1.5M per day per power station) and there is potentially significant risk to life and the environment. The proposed project is to investigate the potential of a multi-frequency electromagnetic (EM) sensor system for monitoring microstructural changes in power generation steels (e.g. boiler plate and pipe) due to high temperature exposure and creep for both in-service monitoring and evaluation during maintenance periods. The work will involve development of a sensor system for long term use at elevated temperatures, and analysis and modelling of sensor signals relative to microstructural changes in the steels.
Planned Impact
In the broadest sense, the societal and environmental benefits will stem from an ability to provide reliable inspection technologies, in-service for high temperature steels. If failure of a power generation plant component occurs, such as the high temperature process plant pipe failure at Flixborough in 1974, the economic impact is severe (an unplanned shutdown is estimated to cost approximately 1.5M per day per power station) and there is potentially significant risk to life and the environment; and of course the broader effects of potential disruptions to supply. Therefore there is a need for reliable and safe operation of high temperature components such as boiler headers and pipe work in the currently operating power generation plant and for the next generation of super critical power stations. The benefits in terms of increased efficiency and reductions in CO2 emissions for super critical power stations are substantial (increasing output efficiencies by approximately 15%, and up to 25 % less carbon dioxide emitted), however the increased risk of component failure requires enhanced inspection technologies. The industrial partners in the projet are four key stakeholders in the supply chain for the new systems. Each of the partners will benefit significantly from the research; for example e-on and Alstom will gain new capability to inspect performance and assess safety critical high temperature components. Corus have seen significant impact from the previous work we have undertaken in this area, in terms of proto-type sensors having been installed in their mills for high temperature microstructural assessment and they will gain further benefit in terms of the scientific understanding generated and the sensor development in this work. TWI will advance their understanding of high temperature NDT of microstructure, which will improve the services they offer to member companies, including within the power generation community. There is significant market potential associated with the sale of monitoring and inspection equipment. The estimated system cost, 30k (based on systems of comparable complexity / importance) for the proposed equipment being developed in this project makes the sensor attractive for multiple installations in power stations, which, coupled with the large number of power stations world-wide indicates significant potential for exploitation, plans for which are already in place based on experience from previous projects. In addition we would reasonably expect spin-off applications to arise in other areas, as we have seen from our previous work.
